Optical time domain reflectometers (OTDRs) usually are employed for monitoring and error analysis of optical fibers and networks. Typically the communication traffic on a segment to be measured is switched off for the measurement. A permanent or at least periodic monitoring allows for an early intervention if degradation occurs and gives advance warning to the network operator before network failure.
More recent networks use multiple wavelengths for data transmission. In some cases transmission takes place in both directions of a line, alternately. For monitoring and characterization or measurement of such a network, a measuring wavelength different from the communication signals (traffic signals) has to be used in order to prevent the measuring signal--i.e. the signal being backscattered or reflected from the network when the measuring wavelength is applied--being distorted or too strongly attenuated for a meaningful measurement.
An object of the invention is to propose a measuring instrument for the measurement of reflected optical signals to test the operational ability of an optical network.